1. Field of the Invention
This invention relates to a continuous, chemical vapor deposition method for producing a coated glass article, particularly, coated architectural glass, and to the coated article so produced. In a specific embodiment, the invention relates to such a method for producing a glass article coated with a layer of silicon formed by treatment with a non-oxidizing gas comprising mono-silane (SiH.sub.4), a silicon oxide layer formed by oxidation of the surface of the silicon layer, and, on the silicon oxide layer, a layer of tin oxide formed by treatment with an oxidizing gas comprising tetramethyl tin. The invention also includes the step of washing the coated glass article with dilute hydrofluoric acid to prevent the formation of a film over the coating during subsequent tempering.
2. The Prior Art
The production of architectural glass coated with silicon formed by continuous chemical treatment with a non-oxidizing gas comprising mono-silane is disclosed in U.S. Pat. No. 4,019,887, "Kirkbride et al.". The method disclosed by Kirkbride et al. is suitable for carrying out one step of the method of the instant invention, namely, that of forming a layer of a silicon coating on a glass article.
The addition of ethylene to the Kirkbride et al. non-oxidizing gas comprising mono-silane is disclosed in U.S. Pat. No. 4,188,444, "Landau", as is the benefit derived from such use of ethylene that the silicon coating has significantly improved resistance to alkali.
The use of tetramethyl tin and other organo tin compounds to produce tin oxide coatings on glass by chemical vapor deposition is disclosed in U.S. Pat. No. 4,187,336, "Gordon".
The production of a glass article having a surface coated with a layer of silicon produced by the method of Kirkbride et al. and additionally coated with a layer of a metal oxide, deposited on the silicon, is disclosed by U.S. Pat. No. 4,100,330, "Donley". The metal oxide layer, Donley discloses, can be formed by spraying the glass article to which the Kirkbride et al. silicon coating has been applied with a solution in a suitable solvent of nickel acetylacetonate, of titanium diisopropyldiacetylacetonate, of dibutyl tin diacetate, or of two or more of cobalt acetylacetonate, iron acetylacetonate, chromium acetylacetonate and nickel acetylacetonate. According to test data in Donley, the Kirkbride et al. silicon coating is removed by both cerium oxide and pumice used according to twenty stroke abrasion tests and by a thirty second immersion in a hot sodium hydroxide solution, while the metal oxide coatings, sometimes applied directly to a glass surface and sometimes over the Kirkbride et al. silicon coatings thereon, are not removed by the procedures of the abrasion tests or by immersion in the hot sodium hydroxide solution.
Most architectural glass is produced by the "Float Glass Process", a part of which is shown in the drawings of Kirkbride et al. This process involves casting glass onto a molten tin bath which is suitably enclosed, transferring the glass, after it cools sufficiently, to rolls that are aligned with the bath, and cooling the glass as it is advanced on the rolls, first through a lehr and, finally, while exposed to ambient conditions. A non-oxidizing atmosphere is maintained in the float portion of the process, in contact with the tin bath, to prevent oxidation, while an air atmosphere is maintained in the lehr.
It will be appreciated that it would be advantageous, when it is desired to coat glass first with silicon and second with tin or another oxide, to do so in conjunction with the production thereof by the Float Glass Process. The glass is at a suitable temperature, as is disclosed by Kirkbride et al., in the float portion of the process for treatment to apply a silicon coating; it is also at a suitable temperature in some parts of the lehr, which contains air, for treatment of a surface thereof with an oxidizing gas comprising tetramethyl tin to form a tin oxide coating on the silicon. However, when gas distributors were installed in a float glass line to treat glass first when it was at a temperature of about 1170.degree. F. (632.degree. C.) and in a non-oxidizing atmosphere, and second when it was at a temperature of about 1125.degree. F. (607.degree. C.) and in air, and glass on the line was treated first with a gas composed of 86 percent by volume of nitrogen, 4 percent by volume of ethylene and 10 percent by volume of mono-silane and second with a gas composed of 99 percent by volume of air and 1 percent by volume of tetramethyl tin, successive silicon and tin oxide coatings were formed on the glass, but the appearance of the coated glass was aesthetically unacceptable because of defects which have been called "pinholes". Overall, the coated glass had a bronze transmitted color and a silver reflective color, but there were numerous, generally circular areas, pinholes, which had a lighter transmitted color.